It is shown that, in the general case, cyclic voltammetric curves of reversible ox/red reactions proceeding in electrodes modified by thick films of electroactive polymers should not satisfy the well-known criteria of the Langmuir adsorption of both ox- and red-particles participating in electrode processes within compact monolayer films. This conclusion follows from the performed analysis of theoretical quasi-equilibrium voltammograms of multilayered films and results from accounting for changes in the electric potential of the film bulk with varying the electrode potential. Concrete expressions of the main parameters characterizing such curves are given for a series of p- and n-doped modifying films.